Geoid Manager
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The Geoid Manager performs tasks for using geoid models with GeoLab. Just about any geoid model can be used with GeoLab through the use of our "Geoid Specification", or GSP, file. The GSP file contains the information needed by GeoLab to interpret the geoid model's binary file, which can be in just about any possible format. Geoid models from around the world are fully supported by GeoLab in this way. |
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Click the "Geoid manager..." button in the Project/Tools tab to display the Geoid Manager dialog. To understand the processes involved with managing and using geoid information with GeoLab, you must keep the following in mind:
Important: A valid geoid specification file always refers to an existing geoid data file. The geoid specification file contains the filename of the geoid data file, so once you have set up a geoid specification file to refer to a specific data file, you should not move the data file.
The Geoid Manager dialog box allows you to load, create, or edit a geoid specification file, and to view the contents of a geoid file.
It contains the following controls:
- A geoid specification file is a file that contains information about the location and contents of a geoid data file;
- A geoid data file is the file referred to in a geoid specification file that actually contains the geoid data (geoid undulations over a specified grid).
Important: A valid geoid specification file always refers to an existing geoid data file. The geoid specification file contains the filename of the geoid data file, so once you have set up a geoid specification file to refer to a specific data file, you should not move the data file.
The Geoid Manager dialog box allows you to load, create, or edit a geoid specification file, and to view the contents of a geoid file.
It contains the following controls:
- New Button: This button allows you to start editing a new geoid file specification.
- Open Button: This button allows you to open an existing geoid file specification.
- Save Button: This button allows you to save changes you have made to the geoid specification file. If the geoid specification file is untitled, you will be prompted for a filename.
- Save As Button: This button allows you to save the contents of the current geoid specification file with another filename.
- Description Edit Box: This edit box allows you to enter or edit a description for the geoid specification.
- Geoid data file Group: This group contains a read-only edit box that displays the currently selected geoid data filename for which you are editing the geoid specification file. The Browse button in this group is presents you with a dialog from which you can select the geoid data file to which the current geoid specification file will refer. The selected geoid file must already exist.
- Linear Unit List Box: This drop-down list box allows you to specify the linear unit for undulations in the geoid data file.
- Ellipsoid List Box: This drop-down list box allows you to specify the reference ellipsoid to which undulations in the geoid file are referred.
- Undulation Type List Box: This drop-down list box allows you to select the type of data (IEEE integer and floating point formats) used in the geoid file for the undulation values. The types are: 2-Byte Int (two byte signed integer); 4-Byte Int (four byte signed integer); 4-Byte Real (four byte real number); 8-Byte Real (eight byte real number).
- Data file layout (bytes) Group: This group contains controls used to specify the structure (all values in numbers of bytes) of the binary geoid data file. These controls are as follows: Header Size Edit Box (allows you to specify the number of bytes in the geoid file that must be skipped over to get to the first geoid undulation record); Record Size Edit Box (allows you to specify the length in bytes of each undulation record in the geoid file. For most geoid files the record size is the same as the size of the undulation data type; Data Offset Edit Box (allows you to specify the number of bytes in each undulation record that must be skipped to get to the first byte of the undulation. For most geoid files the data offset is zero.
- Latitude Major Order Check Box: If this check box is checked, the undulations in the geoid data file must be in "latitude major" order, otherwise they must be in "longitude major" order. In terms of reading a book, when both latitude spacing and longitude spacing are positive, latitude major order means that the undulations are read from left to right (west to east) and from bottom to top (south to north) That is, the "sentences" go from left to right and we read them from bottom to top. Longitude major order in this case (both latitude spacing and longitude spacing are positive) would mean that the undulations are read from bottom to top (south to north), and from left to right (west to east). That is, the "sentences" go from bottom to top and we read them from left to right.
Note that the first undulation in the geoid file is always the value for the from-latitude and from-longitude.
When latitude major order is selected, the longitude is incremented (by the longitude spacing value) across all longitude values, and then the latitude is incremented. If both the latitude spacing and longitude spacing are positive, this would result in starting at the south east corner and proceeding east to west for each latitude until the north west corner is reached. When latitude major order is not selected, the latitude is incremented (by the latitude spacing value) across all latitude values, and then the longitude is incremented. If both the latitude spacing and longitude spacing are positive, this would result in starting at the south east corner and proceeding south to north for each longitude until the north west corner is reached. - Latitudes (d m s) Group: The edit boxes in this group are used to specify the latitude range and spacing as follows: From: This edit box allows you to specify the latitude of the first undulation value in the geoid file. The latitude must be entered in degrees, minutes, and seconds, with an optional leading N or S character indicating north or south latitude respectively; To (This edit box allows you to specify the latitude of the last undulation value in the geoid file. The latitude must be entered in degrees, minutes, and seconds, with an optional leading N or S character indicating north or south latitude respectively; Spacing (This edit box allows you to specify the latitude grid spacing for the geoid file. The latitude spacing must be entered in degrees, minutes, and seconds, with an optional leading plus or minus character. Note that the sign of the latitude grid spacing must be the same as the sign of the to-latitude minus the from-latitude).
- Longitudes (d m s) Group: The edit boxes in this group are used to specify the longitude range and spacing as follows: From (This edit box allows you to specify the longitude of the first undulation value in the geoid file. The longitude must be entered in degrees, minutes, and seconds, with an optional leading E or W character indicating east or west longitude respectively); To (This edit box allows you to specify the longitude of the last undulation value in the geoid file. The longitude must be entered in degrees, minutes, and seconds, with an optional leading E or W character indicating east or west longitude respectively; Spacing (This edit box allows you to specify the longitude grid spacing for the geoid file. The longitude spacing must be entered in degrees, minutes, and seconds, with an optional leading plus or minus character. Note that the sign of the longitude grid spacing must be the same as the sign of the to-longitude minus the from-longitude).
- View Geoid Button: This button will be enabled if the current geoid specification file is valid. The View Geoid dialog will be displayed, allowing you to view the contents of the associated geoid file.
- Close Button: This button closes this dialog. If the current geoid specification file has not been saved, you will be prompted to save it.
- Help Button: This button displays this information.
